Devices capable of producing stable, low noise radio frequency (RF) signals in the MHz to GHz range are highly sought after for a large number of communications applications. Currently, optical frequency combs offer one of the most high-performance ways of generating ultra-low noise RF signals. In order for optical frequency combs to operate, it is necessary for the combs to be octave-spanning to down-convert from higher optical frequencies to lower optical frequencies. For example, the current state of the art is to use an optical frequency comb that spans an entire octave in order to generate an RF signal. The efficiency for this process is low, however, since the majority of the signal is not used and thus requires high power optical pumps.